Because the small size file would spent more over head for file transmitting and make average speed going down, thus a 1GB file would faster than 100 files in 10MB each. Thus recommend via single huge file and able to see the performance. It is like the vehicle fuel usage, in the downtown average mileage lower the the highway. And also we could via FTP to test performance, most FTP client would have average speed log as like the FILEZILLA. https://filezilla-project.org/